Babesia (also known as Nuttallia) is a protozoan parasite that infects red blood cells, causing a disease known as babesiosis (also known as piroplasmosis). Babesia is usually tick-borne (and tick-transmitted) but is also transmissible by transfusion or from mother to child during pregnancy or delivery.
Most cases of babesiosis are asymptomatic and symptoms, if they occur, are non-specific and may include flu-like symptoms (i.e., fever, chills, sweats, headache, myalgia, and arthralgia), hemolytic anemia, or thrombocytopenia. Babesiosis is particularly life threatening in patients with asplenia, weakened immune systems (e.g., due to cancer lymphoma, or AIDS), co-morbodities, such as liver or kidney disease, or who are over the age of 50. In such patients, multi-organ dysfunction, disseminated intravascular coagulation, and even death, may occur (Vannier, et al., Infect. Dis. Clin. N. Am. 29:357-370 (2015)). Babesia parasites reproduce in red blood cells, where they are seen as cross-shaped inclusions and cause hemolytic anemia, not unlike malaria. Due to historical misclassifications, babesiosis has also been known as Texas cattle fever, redwater fever, tick fever, and Nantucket fever. Babesiosis is a malaria-like parasitic disease and is regarded as the second-most common blood parasite of mammals, and has a major impact on the health of domestic animals and humans. Although human babesiosis has historically been uncommon, it is an emerging disease in the Northeastern and Midwestern United States as well as parts of Europe.
Babesia is considered to be the second most commonly found blood parasite of mammals (after trypanosomes). More than one hundred species of Babesia have been identified. The vast majority of transfusion-associated cases of Babesia infection in the U.S. are due to the species Babesia microti, and roughly 2% of reported cases are due to Babesia duncani. Tick-transmission of B. microti mainly occurs in seven states in the Northeast (Connecticut, Maine, Massachusetts, New Hampshire, New Jersey, New York, and Rhode Island) and the upper Midwest (particularly Minnesota and Wisconsin) of the U.S. (see, Herwaldt, et al., Annals of Internal Medicine 155(8):509-520 (2011)). B. duncani, is endemic in the West Coast of the U.S. (see, Herwaldt, et al. (2011)). In 2011, there were 1,124 cases of babesiosis reported in the U.S., of which 10 cases were transfusion-associated (see, Center for Disease Control and Prevention: Morbidity and Mortality Weekly Report 61(27):501-515 (2012)). From 1979-2009, a period spanning 30 years, 162 cases of transfusion-associated babesiosis were reported, at a rate increasing over time (see, Herwaldt, et al. (2011)). Notwithstanding that these statistics may significantly underestimate the true rate of transfusion-associated babesiosis, Babesia is the most commonly transmitted transfusion-associated infection (Leiby, Annals of Internal Medicine 155(8):556-557 (2011)). To date, no Babesia test for screening blood donors has been licensed, and no pathogen-reduction technologies for Babesia are available in the U.S. Although a history of babesiosis infection is a ground for indefinite deferral as a blood donor, many donors may not be aware that they carry the parasite and may have asymptomatic parasitemia and remain infectious for over a year. Further, the Babesia parasite is viable in blood products. The majority of transfusion-associated cases are associated with erythrocytes (including leukoreduced or irradiated units), with a few cases due to platelet transfusion. Prospective testing of blood donations in endemic areas of the U.S. has yielded a 0.38% positive rate for Babesia Moritz, et al., N. Engl. J. Med. 375(23):2236-2245 (2016)).
Because no FDA-licensed screening tests are available, to date, the U.S. blood supply is not currently screened for Babesia. Accordingly, clinicians may miss the diagnosis of transfusion-associated babesiosis, because the clinical presentation is non-specific, and the nationwide distribution of blood products means that cases can occur outside of areas of high Babesia prevalence and outside of peak summer months of tick-borne disease.
Although there are methods (i.e., immunological methods) for detecting Babesia in blood and other tissue and/or biological samples, these methods lack sensitivity and do not accurately predict infectivity of Babesia in blood. Moreover, such immunological methods cannot detect infection during the period when Babesia is present, but has not elicited enough antibodies sufficient for detection. Like other infectious diseases for which blood donations are screened, blood donations must be screened with a sensitive assay to detect Babesia so that infected units may be interdicted and discarded.
In the field of molecular diagnostics, the amplification and detection of nucleic acids is of considerable significance. Such methods can be employed to detect any number of microorganisms, such as viruses and bacteria. The most prominent and widely-used amplification technique is the Polymerase Chain Reaction (PCR). Other amplification techniques include Ligase Chain Reaction, Polymerase Ligase Chain Reaction, Gap-LCR, Repair Chain Reaction, 3 SR, NASBA, Strand Displacement Amplification (SDA), Transcription Mediated Amplification (TMA), and Qβ-amplification. Automated systems for PCR-based analysis often make use of a real-time detection of product amplification during the PCR process in the same reaction vessel. Key to such methods is the use of modified oligonucleotides carrying reporter groups or labels.
Thus, rates of Babesia infection are dramatically increasing within the U.S., with no reliable sensitive assay or means for its detection in samples. Absent a reliably sensitive means for detecting Babesia, the increase in Babesia infection rates, in particular, threatens the safety of the blood donor supply. Therefore, there is a need in the art for a quick, reliable, specific, and sensitive method for detecting and quantifying the presence of Babesia in a sample.